//找到img元素
let pic = document.getElementsByClassName('pic')[0]
console.log(pic)
console.log(pic.innerHTML)
console.log(pic.title)
console.log(pic.className)
//找到btn
let btn = document.querySelectorAll('.btn')
btn.onclick = function () {
    pic.src = '../img/desktop.jpg'
    pic.style.widtn = '300px'
    //获取页面内容
    console.log(app.innerHTML)
}
let btn1 = document.querySelector('.btn1')
let i = 0
btn1.onclick = function () {
    i++
    let box = document.querySelector('.box')
    //是拼接还是覆盖
    box.innerHTML = i + 'hello world!<br>'
}